Actuators are used in a variety of applications to control to one or more aspects of an industrial process. For example, actuators are used to operate mechanical valves that regulate the flow of materials in such diverse applications as automobile fuel injectors, hydraulic servovalves, and ink jet printer nozzles. One particular type of actuator is a piezoelectric actuator, which is a nano-positioning device that deforms its shape in response to a stimulus of electrical charge
In gas delivery applications, particularly those involving high-speed processes, the time required to actuate a control valve can directly affect the performance of a mass flow controller. A typical mass flow controller product stimulates a piezoelectric actuator by transferring charge from a power source to the actuator load. Charge transfer rate can be increased by increasing the peak current. The speed of charge transfer is limited, however, by peak current stresses placed on the internal bond wires connecting the drive circuit to the piezoelectric actuator, as well as by practical considerations of the cost, size, and electrical isolation of high-current switches and other components.
As a result, contemporary mass flow controller devices tend to have relatively slow actuation times—on the order of several hundred milliseconds. For many process applications, these actuation times impose an undesirable lower limit on the open time, or upper limit on the repetition rate at which the controller may be operated.
As an alternative to in-line mass flow control, a mass flow diverter may be employed in applications requiring higher speed control of minute feed gas quantities. In this approach, a pneumatically actuated valve is located on a gas stream conduit venting continuously from, a source. To inject a quantity of gas into a process, the valve is driven rapidly to a position that diverts the stream into the process environment, and then returned rapidly to the venting position. Use of high-speed pneumatics to drive the diverter valve allows For short actuation times (on the order of tens of milliseconds) and therefore greater control over the delivered gas quantity. In addition to the added cost and complexity of this approach, another significant disadvantage is that the vented material often cannot be recovered due to contamination concerns. For many processes, particularly in the manufacture of semiconductor devices, this can result in significant waste of expensive reed gas materials along with all attendant need for scrubbing or abating greater quantities of the gases downstream of the process.
Although present devices are functional to an extent, they are not sufficiently responsive or otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.